It is well known in the coated abrasive art to apply a resinous binder and abrasive grains to a paper or cloth backing material (the "backer") and then to cure the binder to produce a coated abrasive product. Typically, one or more overcoats (the "size" coats) are applied over the grain carrying layer (the "make" coat) and, in turn, cured. The use of radiation curing technology, e.g., electron beam technology, to fix abrasive grit to certain substrates such as paper and cloth is known in the art. Systems for commercially applying such radiation curing, e.g., electron beam curing technology, to the manufacture of coated abrasives are disclosed and explained in U.S. Pat. Nos. 4,345,545 and 4,385,239. Electron beam curable resin systems applicable to the electron beam manufacture of coated abrasive products are also well known as disclosed and explained in U.S. Pat. Nos. 4,457,766; 4,547,204; and 4,588,419. These patents teach the use of urethane oligomers as radiation curable resin systems, e.g., electron beam curable resins, in the fixing of abrasive grits to substrates such as webs (backers) of paper and cloth.
The application of mineral particles to a polyvinyl chloride floor matting material is discussed in U.S. Pat. No. 4,336,293. In this reference, a polyamide primer is applied to a silicone impregnated kraft release paper. Then a heat curable liquid polyurethane make resin is coated onto the polyamide primer. This composition is then partially thermally cured by running it through an oven at 120.degree. C. for 30 minutes. Once it is partially heat cured, the mineral particles are applied and a size coating, e.g., the same composition as the make coat, is spread on and the composite again run through an oven at 130.degree. C. for 4 hours to fully thermally cure it. In the formation of the composite, the polyamide "prime coating" is a "hot melt adhesive resin." The composite, still on the kraft release paper which is necessary to preserve the form of this intermediate product which would otherwise be subject to severe thermal distortions, is then concurrently fed, in sheet form, into an extruder along with hot, melted polyvinyl chloride (in liquid form) which adheres or bonds to the polyamide "prime coating" to glue the polyamide, as a hot melt adhesive, to the solidifying surface of the polyvinyl chloride which forms the backer. The kraft release paper is peeled off as the composite is laminated to polyvinyl chloride substrate material, the combination which then forms the floor matting. The composite may be embossed, on the side opposed to that receiving the backer layer, at the same time it is coated with the backer. The invention described is severely restricted in its choice of backer in that distortions in use as a result of temperature cycling and stretching forces restrict the materials that can be used. Additionally the use of the kraft paper layer which is subsequently discarded involves necessary complications, without which however the process would not work.
U.S. Pat. 4,196,243 teaches the formation of a "plastic wear layer" on a polyvinyl chloride substrate having a thickness in the range of about 50-250 mils. Ultraviolet light is used to cure the polyurethane make and size coatings which are used. The make and size resin systems must be modified by the addition of "photosensitizers" which are sensitive to the wave length and energy level of the ultraviolet light source that is being applied.
U.S. Pat. 4,608,287 shows the formation of an "abrasive" coating on a "plastified" polyvinyl chloride film of 0.05 mm in thickness. The polyvinyl chloride film, itself, has a paper sheet adhered to its opposite surface by a pressure sensitive adhesive. A chalk extended polyoxpropylene glycol/diphenylmethane diisocyanate (polyurethane) resin system is applied to what is to be the "abrasive" coated side of the polyvinyl chloride backer. Granulated polyurethane, as the "abrasive" material, is then spread on top of the resin system, and the composite is put into a hot air drying oven at 80.degree. C. for 5 minutes "to accelerate cross-linking." A second example in this reference shows the use of a non-woven fabric layer backer bonded with an acrylic resin. On this fabric layer backer, a coating of heat curable "synthetic rubber based adhesive" is formed. Then, on this synthetic rubber layer, a diphenylmethane diisocyanate (70% aliphatic solvents) layer is formed, onto which is spread granulated polyurethane powder. This formed composite then is put into an oven at 80.degree. C. for 7 minutes to "cross-link" the resin by " evaporation of the solvents." Following this, a second coat of the polyurethane resin (this time with 30% aliphatic solvents) is spread on, and the composite is placed back into the oven at 80.degree. C. for another 7 minutes. This second resin layer is said to provide "an anti-dirt protective film" and to "increase the abrasive strength." In this second example, no polyvinyl chloride is used.
Polyvinyl chloride has a relatively low softening point, thus rendering it unsuitable, as a backer material, for use in conventional thermal curing techniques for producing coated abrasive products. The radiation curing techniques, as explained in several of the above cited references, do not use the application of heat, per se, as the primary means for curing resins. Thus, the heat generated in the electron beam resin curing processes, although existent, does not reach the levels wherein polyvinyl chloride materials, especially in relatively unsupported thin sheet form, are rendered overly softened, melted or decomposed. The electron beam resin curing techniques are especially suitable for application to production of the products of the present invention. In particular, U.S. Pat. Nos. 4,345,545; 4,385,239; 4,457,766; 4,547,204; and 4,588,419 are specifically included herein by this reference in respect to their respective pertinent description and discussions of the relevant factors applicable to the electron beam formation of coated abrasives and variants thereof.
These, and other features of the present invention can be more readily comprehended from a reading of the cited references, and the following text of the specification, as well as from the claims hereinafter appended .